Cellulose insulation is typically manufactured from recycled paper and cardboard. The U.S. government requires that all cellulose insulation meet ASTM C-739. This mandate requires testing for critical radiant flux (CRF) (flame), smoldering combustion, odor emission, corrosion, thermal resistance (R-value), fungi resistance, and moisture absorption. In addition to these tests, off-gassing of ammonia or the toxicity of boric acid are problems that need to be addressed. The air-borne dust generated during the installation of cellulose insulation creates an unpleasant working environment for installers and presents an infertility issue in cases where borates are used. Borates are used in 99% of cellulose insulation. While removal of dust from cellulose insulation rectifies many problems, there remains the problem of disposal of the dust.
Burning or combustion of cellulose fiber materials such as paper, cardboard, etc., generally involves two different chemical processes: a) flaming, which results from ignition of gases released by pyrolysis of the cellulose fiber material, and b) smolder, a slow, high temperature, flameless combustion which results from oxidation of the remaining carbon-rich material, as with charcoal in a barbeque.
Cellulose insulation is flammable and prone to smoldering. However, specific chemical additions to a paper material will increase its resistance to burning. Some chemicals will extinguish flaming but not smoldering combustion. Examples of such flame-only extinguishing chemicals include borax pentahydrate, hydrated magnesium sulfate, aluminum trihydrate, and ammonium sulfate, among others. Other chemicals can extinguish both flaming and smolder. Examples of these chemicals include ammonium sulfate and boric acid.
Although there are many chemicals that extinguish flaming, to date, boric acid is the only known economically viable chemical that can effectively extinguish smolder. Boric acid is the primary smolder inhibitor. The two fire-retardant formulas in almost exclusive use today in the cellulose insulation manufacturing industry are: a) 1 part boric acid to 2 or 3 parts ammonium sulfate (60%), and b) 1 part boric acid to 2 to 3 parts borax (35%). The remaining 5 percent of industry products will always use boric acid (as smolder inhibitor) with other flame inhibitors such as Epsom salts, etc. Without boric acid, smolder could not be guaranteed to be prevented, and in order to market cellulose insulation products, the U.S. government mandates the prevention of smolder.
Borates and ammonium sulfate represent 95% (by weight) of all the flame retardants used by the cellulose industry but their future use is in doubt because of government restrictions. France has banned the use of ammonium sulfate because of ammonia out-gassing and consequent problems. Europe is expected to follow. There are growing concerns about potential adverse health effects associated with the use of and exposure to borate compounds (e.g., borax, boric acid, etc.), which, although providing fire retardant and insecticidal properties, are respiratory irritants and have shown to have adverse reproductive effects in test animals. Europe banned the use of any borate compound due to fears of infertility. Pleas from the cellulose industry lead to the European Union (EU) giving a 2-year allowance to use borates but restricted its use to 5% by weight of the finished product. The U.S. government has these two problems under consideration but until a conclusion is reached it is required for manufacturers to inform users of its products that they could interfere with reproduction.
Testing for flaming is carried out using critical radiant flux (CRF) equipment. In that test, a “pass” is achieved if the cellulose material will not support surface burning while being subjected to radiation of 0.12 watts/cm2 or less. Smolder testing is performed by positioning a lighted cigarette into a sample of insulation at settled density contained within a 9″×9″×4″ open-top stainless steel box. The sample is left for 2 hours after which it is considered to be a pass if it loses less than 15% of its original weight.
In Europe, various classifications are available ranging from Category A to Category F. Chemical loading that allows cellulose insulation to meet ASTM C-739 would also allow it to meet a Category B. To obtain a Category C listing, lesser amounts of chemical can be used than required under ASTM C-739 standards.
In order to prevent flaming and smoldering combustion, most cellulose insulation is manufactured by applying fire retardant chemicals in powder form, for example, hydrated borax, boric acid, ammonium sulfate, aluminum trihydrate (ATH), etc. In order to meet government standards for cellulose insulation, the loading of a powdered chemical is typically about 14% to 18% by weight (wt %) of the final insulation product. However, powdered chemicals are relatively expensive and their inclusion significantly raises the costs associated with the manufacture of a cellulose insulation product.
In addition, applying fire retardant chemicals only in powder form dusts the cellulose particle surface, with a large portion of the powder being present in the product as loose dust particles, requiring high loadings of chemical and higher costs. By comparison, the application of a liquid form of the fire retardant chemical will penetrate the cellulose particles and thereby require lower loading of the fire retardant chemical. This application of liquid fire retardant chemical can lower raw material cost to result in appreciable cost savings. Liquid fire retardant compositions are described, for example, in U.S. Pat. Nos. 4,595,414 and 4,168,175 (Shutt). Examples of liquid fire retardant chemicals include aqueous solutions of ammonium sulfate, monoammonium phosphate, diammonium phosphate, ammonium tripolyphosphate, boric acid, ferrous sulfate, zinc sulfate, and mixtures thereof, dissolved in water. Of those chemicals, ammonium sulfate is the most popular due to its low price and high solubility in water.
A disadvantage of currently known liquid fire retardant chemicals is that they can be corrosive and/or devolve ammonia through off-gassing. In addition, as discussed above, exposure to borate compounds has been linked to potential adverse health effects.
Corrosion under insulation (CUI) is corrosion that develops over time beneath thermal insulation used, for example, on pipes, tanks and various manufacturing and process equipment. CUI typically results from condensation, rainwater, cleaning fluids, etc., that seep in and permeate into the insulation and onto the underlying substrate and subsequently cause off-gassing of ammonia resulting in corrosion of pipes, etc., and damage to the substrate.
Accordingly, it would be desirable from an industry standpoint to provide a cellulose material that would overcome the foregoing disadvantages. It would also be desirable to produce such a cellulose material at a low cost, with liquid chemical as the sole flame retardant which will possess the requisite level of fire retardance to meet various government regulations and standards.